Employees of the U.S. National Security Agency spied on "unfaithful" husbands, boyfriends and girlfriends using surveillance technology of the agency, according to a letter from the NSA to a U.S. Senator.

The letter from NSA Inspector General George Ellard, released Thursday by Senator Charles E. Grassley, cites 12 "substantiated instances" of the intentional misuse of the signals intelligence (SIGINT) powers of the NSA.

The misuse of NSA authorities for romantic purposes, popularly known as Loveint, was cited in various media reports as an instance of widespread compromise of people's privacy by the NSA. The Wall Street Journal reported in August that NSA officers had used the agency's "enormous eavesdropping power to spy on love interests." But General Keith Alexander, director of the NSA, on Thursday described the "claimed evidence of thousands of privacy violations" as false and misleading.

"According to NSA's independent inspector general, there have been only 12 substantiated cases of willful violation over 10 years -- essentially one per year," Alexander told a hearing on Foreign Intelligence Surveillance Authorities of the U. S. Senate Select Committee on Intelligence. "Several of these cases were referred to the Department of Justice for potential prosecution, appropriate discipline action in other cases. We hold ourselves accountable very day."

Among the cases cited in the NSA letter to Grassley is one of an employee who spied from about 1998 to 2003 nine telephone numbers of female foreign nationals without a "valid foreign intelligence purpose," and listened to collected phone conversations while assigned to foreign locations. The employee also collected the communications of a U.S. person on two occasions.

In another instance in 2004, an employee of the NSA tried "out of curiosity" a query of his home phone number and the phone number of his girlfriend, a foreign national. Although he was blocked by the system from collecting information on his phone as it was made on a U.S. person, he managed to retrieve metadata of his girlfriend's calls.

The NSA is under scrutiny after former contractor Edward Snowden disclosed that the agency was collecting records in bulk of Verizon phone customers and also had real-time access to the servers of Internet companies, a charge the companies have denied. Such dragnet surveillance is likely to lead to misuse of privacy, privacy groups have argued.

Grassley wrote in August to Ellard for details about intentional and wilful abuse of NSA surveillance powers.